Spin-on filters have been employed in a variety of applications including hydraulic systems and engine lubrication systems. Such filters generally include a filter element within a can or housing having a cover or attachment plate at one end thereof by which the filter can be screwed onto or off a filter head. A central opening and several surrounding openings in the cover direct flow through the filter and filter element therein, which flow can be in either an inside/out or outside/in pattern. A circular gasket on the outside of the cover serves as the external seal between the filter and filter head, while another circular gasket on the inside of the cover functions as the internal seal between the filter element and cover. A spring is often provided in the lower end of the housing to maintain the filter element in sealing engagement with the cover. Spin-on filters are typically intended to be used only once before removal and replacement.
Although satisfactory in low and medium pressure applications, the spin-on filters of the prior art have not been particularly suitable for use in high pressure applications, such as in hydraulic transmission pumps, where spikes or surges up to about 1000 psi can occur. Most of the spin-on filters currently available are adaptations of the type used in engine lubrication systems. The covers of the spin-on filters available heretofore are typically constructed of a stamped steel base disc and a relatively thinner secondary disc spot welded thereto. The base disc includes an extruded, relatively shallow, internally threaded neck portion by which the filter can be connected to a filter head. Flow openings are punched into the base disc around the neck portion. The lip at the open end of the housing is connected by means of a lock seam to the periphery of the secondary disc, which is also formed to serve as a seat for the external gasket. In this design fatigue failure is most likely to occur at the rolled lock seam or at the spot welds. A burst failure is most likely to occur either upon bending of the cover which allows leakage past the external gasket, or upon unfolding of the rolled lock seam. The prior spin-on filters have thus been susceptible to failure at the cover and/or at the connection between the cover and housing.
Various attempts have been made to strengthen and otherwise increase the pressure capacities of the prior spin-on filters. Different materials and/or increased material thicknesses thereof have been used, improved lock seams have been developed, and reinforcing profiles have been formed into the cover plates. These efforts have resulted in increasing the burst capacities of such spin-on filters up to about 500 psi, and have therefore been of some success; however, even the current filters having a 500 psi burst capacity have been found marginal in certain applications. Manufacturing limitations also exist for the thickness of material which can be punched or press formed to construct spin-on filters according to conventional techniques.
There is thus a need for an improved spin-on fluid filter of high strength construction capable of withstanding pressure surges and spikes up to about 1000 psi or more.